Stabilized ammonium perchlorate

ABSTRACT

THE PRESENT PATENT DESCRIBES NOVEL AMMONIUM PERCHLORATE IS STABILIZED WITH AN EFFECTIVE STABILIZING AMOUNT OF AN AMMONIUM, ALKALI OR ALKALINE EARTH METAL TRIMETAPHOSPHATES, TETRAMETAPHOSPHATES AND POLYMETAPHOSPHATES. TYPICAL STABILIZERS ARE (NAPO3)X LINEAR (SODIUM POLYMETAPHOSPHATE), NA4P4O12 (SODIUM TETRAMETAPHOSPHATE), NA3P3O9 (SODIUM TRIMETAPHOSPHATE). CA2P4O12 (CALCIUM TETRAMETAPHOSPHATE) AND (NH4)4P4O12 (AMMONIUM TETRAMETAPHOSPHATE).

United States Patent 3,795,555 STABILIZED AMMONIUM PERCHLORATE David 0. Depree, Loomis, Calif., assignor to Aerojef- General Corporation, El Monte, Calif. No Drawing. Filed June 22, 1970, Ser. No. 48,777

Int. Cl. C06b 11/00 US. Cl. 14976 4 Claims ABSTRACT OF THE DISCLOSURE The present patent describes novel ammonium perchlorate is stabilized with an effective stabilizing amount of an ammonium, alkali or alkaline earth metal trimetaphosphates, tetrametaphosphates and polymetaphosphates. Typical stabilizers are (NaPO linear (sodium polymetaphosphate), Na P O (sodium tetrametaphosphate), Na P O (sodium trimetaphosphate), Ca P O (calcium tetrametaphosphate) and (NH P O (ammonium tetrametaphosphate) BACKGROUND OF THE INVENTION Organic ammonium perchlorates are excellent explosives. The stability of these compounds in such applications is important for several reasons. In applications where high temperatures are involved, the temperature stability of the compounds is particularly critical. In another aspect, the stability of these compounds is important in allowing valuable time for evacuation or for fire fightin g under certain circumstances such as the aircraft carrier fires. In warfare, there have been a number of occasions in recent years where an explosive charge containing a perchlorate was inadvertently exposed to burning kerosene, gasoline or napalm. Under such circumstances, the onset rate of rapid exothermic decomposition of the perchlorate determines to a large degree whether or not an explosion can be averted.

The instability of ammonium perchlorate at high temperature has been well established and has been found to vary significantly from lot to lot. However, good ropellant performance is available from ammonium perchlorate, and only ammonium perchlorate supplies the energy required to achieve the performance levels required for air launch motor propellants. Even at temperatures as low as 350 F. ammonium perchlorate undergoes a significant amount of decomposition. Because the decomposition of ammonium perchlorate below deflagration temperatures is indicated as proceeding first through dissociation into ammonia and perchloric acid, a severe oxidative attack on binder ingredients by perchloric acid can be anticipated. Studies with as received ammonium perchlorate have shown that at temperatures in the range of 250 to 280 C. a relatively rapid decomposition of ammonium perchlorate proceeds to a weight loss of 25 to 35% and then tends to stop. The resultant oxidizer is a porous material with decomposition apparently occurring at imperfection or impurity sites. At these sites catalysis of the decomposition of the surrounding ammonium perchlorate appears to occur. A lot to lot variation in both the degree and rate of decomposition has been observed.

Previously, various stabilizers including sodium orthophosphate have been proposed for ammonium perchlorate and organic-substituted ammonium perchlorate. However, none of them have proved to be as effective as the novel stabilizers of the present invention. More specifically, we have now discovered that the ammonium, alkali and alkaline earth metal metaphosphates, and the ammonium fiuorophosphates are surprisingly effective in increasing the stability of the ammonium perchlorate and organic ammonium perchlorates. Accordingly, it may be 3,795,555 Patented Mar. 5, 1974 anticipated that the stabilized ammonium perchlorate and organic ammonium perchlorates of the present invention will find a wide application in the propellant and explosive arts.

SUMMARY OF THE INVENTION Briefly, the present invention comprises novel ammonium perchlorates stabilized with an effective stabilizing amount of an ammonium, alkali or alkaline earth metal trimetaphosphates, tetrametaphosphates and polymetaphosphates. Typical stabilizers are (NaPO linear (sodium polymetaphosphate), Na P O (sodium tetrametaphosphate), Na P O (sodium trimetaphosphate),

(calcium tetrametaphosphate) and (NH P O (ammonium tetrametaphosphate). This invention also comprehends novel composite explosives containing the abovedescribed stabilized compounds.

It is an object of the present invention to provide a novel class of stabilized ammonium perchlorates.

Another object of the present invention is to provide stabilized compositions which are capable of withstanding exposure to higher temperatures and which have improved safety.

Still another object of this invention is a class of novel composite explosives containing ammonium perchlorate and/or organic ammonium perchlorates stabilized with ammonium, alkali or alkaline earth metal metaphosphates.

These and other objects and advantages of this invention will be apparent from the more detailed description which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS The present invention is applicable to the stabilization of all types of ammonium perchlorate and organic ammonium perchlorates such as ethylenediammonium diperchlorate, dimethyl ammonium perchlorate, trimethyl ammonium perchlorate, ethyl ammonium perchlorate, diethyl ammonium perchlorate, and the like.

In general, the stabilizers of this invention are used in an effective stabilizing amount usually on the order of from about 0.1% to about 3%, by weight based on the weight of the solid ammonium perchlorate. The stabilizer may be incorporated in the perchlorate explosive by blending using conventional mechanical mixing equipment. The same result can be achieved in many cases by a simple modification of the process used to produce perchlorate explosive, such as spraying a solution of the stabilizer onto the wet perchlorate before drying.

The following examples are presented solely to demonstrate the invention and should not be regarded as limiting in any way.

To doubly recrystallized methylammonium perchlorate was added 0.5% of each of the following additives:

Example No.: Additive 1 (NaPO linear. 2 N33P30g. 3 Ca2P4O 2- 4 N34P4012. 5 (NH4)4P4O12- Upon heating these compositions, it was found that the first exotherm occurred at a significantly higher temperature than the exotherm characteristic of unstabilized methylammonium perchlorate.

EXAMPLE 6 In this example, 0.5% ammonium tetrametaphosphate was added to methylammonium perchlorate. This addition was found to increase the decomposition temperature of methylammonium perchlorate from 290 C. (554 3 F.) to 340 C. (642 F.), based on diflerential thermal analysis data.

The composite explosives of this invention is preferably of the castable type and contain the stabilized organic ammonium perchlorate, a metallic fuel such as aluminum powder, and a liquid curable polymeric binder such as a polyurethane, epoxy, polyester, vinyl, ether, acrylate, silicon or other polymers. These materials are mixed in conventional mixing equipment, cast, and cured to form the solid composite explosive. The binders applicable to the practice of this invention are well known in the art, and need not be described in detail in this patent.

The composite explosive can be made in the form of sticks, pellets, and the like. This invention also comprehends explosives in the form of liquid slurries and gelled liquids.

The following examples illustrates a pelletized explosive.

EXAMPLE 7 The following ingredients are mixed.

Ingredient: Weight percent Methylammonium perchlorate stabilized with 2% of N34P4012 Calcium stearate (pelletizer lubricant) 3 Polyether polyol-toluene diisocyanate polyurethane binder The ingredients are mixed with the diisocyanate and urethane catalyst (ferric acetylacetonate) being added last. The material is then pelletized and the pellets cured by heating at about 130 F.

In a preferred embodiment, the stabilization process consists of (1) purification of ammonium perchlorate to reduce the concentration of impurities. This can be achieved either by recrystallization or selective reduction of the chlorate impurity, (2) either treatment of the purified ammonium perchlorate in a coating operation with a concentrated solution of the metaphosphate stabilizer at a concentration of less than 1% of the ammonium perchlorate or (3) incorporation of less than 1% of dry finely divided metaphosphate stabilizer in a blending operapellant prepared with these ingredients shows, that (1) as received ammonium perchlorate exhibits a strong exotherm initiating at about 300 C. which is related to the concentration of chlorate impurity and (2) that the de-flagration temperature of the composite propellant occurs at essentially the onset of this exotherm.

Recrystallization or purification of ammonium perchlorate reduces this impurity exotherm but has little influence on the onset temperature. According to this invention, it has been found that the addition of small concentration of alkali, alkaline earth as well as ammonium metaphosphates resulted in a shift of the onset of the first ammonium perchlorate exotherm to higher temperatures. The relative shifts produced by linear sodium metaphosphate polymer, trimetaphosphates and tetrametaphosphates with recrystallized ammonium perchlorate are shown in Table I.

TABLE I. --EFFECT OF VARIOUS METAPHOS- PHATE ADDITIVES ON THE FIRST EXOTHERM IN THE DIFFERENTIAL THERMAL ANALYSIS OF AMMONIUM PERCHLORATE (0.5% additives, doubly recrystallized ammonium perchloroate, heating rate 20 C./min.)

Initiation of first Additive: exotherm, F. None 590 Na PO (sodium orthophosphate) 640 (NaPO linear 660 N33P309 Na P O Q4 4 12 712 TABLE II.RELATIONSHIP OF THE SHIFT OF THE ONSET OF THE FIRST EXOTHERM IN DIFFERENTIAL THERMAL ANALYSIS OF AMMONIUM PERCHLORATE TO PROPELLANT HIGH TEMPERATURE STORAGE STABILIT Efiect on storage stabilityof propellant 1 6 hrs. at 350 F. 1 hr. at 450 F.

Effect on AP onset Change in Chance in on first Weight hardness, 2 Weight hardness, 2 Addltlve exotherm, los Shore A loss, Shore A. F percent units percent units None (as received AP) 590 None (recrystallized ammonium perchlorate) 590 0.060 22 0. 52 22 640 0. 058 18 0. 17 15 3 600 0. 055 11 0. 5 (NH4)4P4O12 710 0. 043 7 0. 22 9 1 Unplasticized carboxy-termiuated polybutadiene/epoxy binder, aluminized propellant (80% solids) 1 inch propellant cubes, stored in air.

2 Stored for 4 hrs. Final shore measurement taken at center of cube. I Questionable value, based on necessity for dry mixing ammonium perchlorate and additive.

tion with ammonium perchlorate. The increased effectiveness of the metaphosphate stabilizers is demonstrated by dilferential thermal analysis measurements of the shift of the onset of the first exotherm of ammonium perchlorate and improved ammonium perchlorate propellant storage stability at 350 and 450 F., as indicated by Shore A hardness and weight loss data. The use of these stabilizers also provides stability for propellants containing burning rate additives such as iron oxide.

The relative thermal stability of propellant and propellant ingredients may be measured by differential thermal analysis. A comparison of the differential thermal analysis conducted at a heating rate of 20 C./min., of typical as received ammonium perchlorate. An imino cured carboxyl A comparison of the oxidizer differential thermal analysis data with the storage behavior of one inch propellant cubes at 350 and 450 F. indicates that storage capability is related to the onset temperature and the magnitude of the first exotherm observed in the differential thermal analysis. The measurement of changes in Shore A hardness for one-inch propellant cubes prepared with as received, recrystallized and recrystallized stabilized ammonium perchlorate show an order of stability in general agreement with that predicted from the differential thermal analysis measurements.

Having fully described the invention, it is intended that it be limited only by the lawful scope of the appended terminated polybutadiene binder and an aluminized proclaims.

I claim:

1. Ammonium perchlorate stabilized with an effective stabilizing amount of an ammonium, alkali or alkaline earth metal metaphosphate.

2. Ammonium perchlorate stabilized with an eifective stabilizing amount of a compound selected from the group consisting of (NaPO linear (sodium polymetaphosphate), Na P O (sodium tetrametaphosphate), Na P O (sodium trimetaphosphate), Ca P O (calcium tetrametaphosphate) and (NH P O (ammonium tetrametaphosphate).

3. The composition of claim 1 wherein the stabilizer is ammonium tetrametaphosphate.

3,147,160 9/1964 McCrone 149-76 X 3,172,793 3/1965 Markowitz 23-85 X 3,269,879 8/1966 Stammler et al 14976 X CARL D. QUARFORTH, Primary Examiner E. A. MILLER, Assistant Examiner US. Cl. X.R. 423265, 476 

